Rotary compressor or engine having a variable compression ratio



April 6, 1965 v M. E. BowmsH 3,

ROTARY COMPRESSOR OR ENGINE HAVING A VARIABLE COMPRESSION RATIO Filed Dec. 24, 1962 s Sheets-Sheet 1 INVENTOR MPED/TH E. EOWD/fi'l/ April 6, 1965 M. E. BOWDISH ROTARY COMPRESSOR OR ENGINE HAVING A VARIABLE COMPRESSION RATIO Filed Dec. 24, 1962 3 Sheets-Sheet 2 A rraen/[VS A ril 6, 1965 I M. E. BOWDISH Filed Dec. 24, 1962 5 Sheets-Sheet 3 I g t I 9 .5. 2 50' ab i 46 i I INVENTOR. Ama a/2w 7 EaWD/JW 39 KM 1 who A rrO/eA/EVJ United States Patent 3,176,908 RGTARY COMPRESSOR 0R ENGINE HAVING A VARIABLE COMPRESSIQN RATIO Meredith E. Bowdish, R0. Box 2011, Anchorage, Alaska Filed Dec. 24, 1962, Ser. No. 246,781 13 Claims. ((Il. 236-438) This invention relates to rotary devices of the character described in my US. Patent 3,181,700 of August 27, 1963 which is entitled Rotary Compressor or Engine." The invention constitutes an improvement over my earlier devices and has a principal object of providing a means whereby the compression ratio of such devices can be varied. Other objects include providing for larger intake and exhaust ports in such devices and designing or adapting them so that in general the operating fluid can move more freely between the ports and the operating core of the particular device.

It will be recalled from by patent that the devices to which I refer include a housing defining a walled chamher, and a pair of rotors one of which is in the form of a grooved disc rotor and the other of which has a bladed hub construction. The rotors are rotatably mounted in the chamber in end-to-end relationship with their axes of rotation intersecting one another at an acute angle. .They are also mounted so that the hub portion of the hub rotor is cooperatively engaged with one end of the chamher in forming a rotational seal thereacross. The adjacent ends of the rotors are also cooperatively engaged in forming a seal thereacross, more aptly described as a sliding seal in the operational context of the device. And furthermore the perpihery of the disc rotor is cooperatively engaged with the wall of the chamber in forming a rotational seal thereabout, so that in the final analysis the two rotors together define an annular operating well with the chamber wall portion lying between the end of the chamber and the periphery of the disc rotor.

The grooves and blades of the rotors, it will also be recalled, are arranged at angular intervals about the opposing end faces of the rotors and are cooperatively engaged in forming a series of radially oriented cells at the intervals. The cells sweep through the well during the conjoint rotation prescribed for the rotors, and are subjected on opposite sides of the well to alternate stages of volumetric expansion and contraction characteristic of the intake and compression stages of a two cycle compressor or engine. The latter results from the fact that the end faces of the rotors are substantially centered at the intersection of the axes and at least one of these faces has aconical section whichris inclined at the aforementioned acute angle with respect to the other so that when the rotors are conjointly rotated, the faces alternately converge and diverge between opposite angular stations at which they diverge to a maximum and coincide, respectively. A useful result is obtained by supplying a fluid to a port opening into the expansion or intake side of the well, and exhausting the fluid through a second port opening from the other side of the well where the cells undergo the compression stage.

Of course if compression is to be maintained in the latter stage, provision must be made for guaranteeing the integrity of the individual cells during their passage through this other side of the well. My aforementioned patent describes an inventive means and technique by which a sliding seal can be obtained between the blades and the grooves. The integrity of the cells is maintained otherwise by the convention of closing the aforementioned chamber wall portion about the imaginary surface generated by the edges of the blades as they rotate, to the extent that a rotational seal is acquired between the edges and the wall.

The present invention departs from this convention in that at least a part of the chamber wall portion is recessed back from this imaginary surface to a greater extent than required in rotational engagement and in fact to the extent that a part-annular channel is formed between the wall and the blades. Of course, the chamber Wall portion remains operatively closed throughout the sector of the well lying between the angular stations at which the supply port terminates in the intake side of the well and the exhaust port commences in the compression side of the Well. Thechannel is formed on the compression side of the well and extends from an intermediate angular station adjacent to the station of maximum divergence to at least the angular station at which with the exhaust port commences so that if not otherwise blocked, the fluid would or could flow from this intermiate angular station to exhaust without the necessity for transport in the cells. To prevent this, however, a filler element of comparable cross section is operatively positioned in the channel adjacent the intermediate angular station. By comparable cross ection it is intended that the tiller element be given substantially the same depth and span as the channel itself so that the filler and the blades again provide a rotational seal between the cells. This term is, however, a reference to the maximum cross section of the filler element inasmuch as it may be desirable, for reasons which will become apparent, to give the tiller element a sloping or stepwise configuration along the length of the channel. I

Now, it will be appreciated that the spacing of the filler element from the angular station at which the exhaust port commences determines the compression stroke of the device, for once the element terminates, fluid can move freely along the channel to exhaust. Accordingly, the invention employs the filler element as a means for varying the compression stroke by providing that its cross sect-ion is also such that it can slide relatively into and out of the channel for purposes of adjusting its position with respect to the latter station. The element may comprise a single arcuate leaf or a plurality of such leaves. These may be slidably engaged in the chamber wall portion to move relatively inwardly and outwardly of the compression side of the channel from within the wall itself. Or in the alternative, the channel may be made to extend through the station of maximum divergence into the intake side of the well, and the leaf or leaves slidably engaged along the length of the channel to move relatively inwardly and outwardly of the compression side of the channel from within the intake side of it. This latter technique has the advantage of varying the intake volume in inverse relation to the adjustment made in the compression stroke. It therefore is the preferred mode of practicing the invention at the present time, and is employed in most applications using a single leaf form. This single arcuate leaf form will be illustrated more specifically hereafter.

The channel can be positioned opposite the open end faces of the cells, opposite the radial faces of the cells, or if desired opposite both faces in, for example, an L-shaped configuration. This will depend on the configuration of the blades themselves and the sensitivity of control that is desired in practicing the invention. It is also contemplated that the edges of the blades may be entirely curvilinear in form and that the channel can lie opposite a part or the Whole of the single open face now characterizing the cells. conceivably too, the periphery of the end face of the disc rotor may be rabbeted to form another open end face for the cells, and in such event the channel can be positioned opposite the annular rabbet so formed in the disc rotor.

Another feature of the invention calls for opening the exhaust port into the channel itself so that the filler element can be moved to positions transverse the opening of drawing wherein: r

it will be noted that the rotor 18 has a series of grooves or recesses 35 formed in the end face 36 and that the rotor 20 has a corresponding series of blades or'vanes 37 in its opposing endface as comprised by the face 26 of the disc base 26 of the dome 2d. The grooves and blades are arranged at angular intervals about the end FIGURE 1 is an exploded isometric view of the in,-

dividual partsof a rotary compressor embodying the ini 'venti-on, with a portion of the casing or housing being broken away to illustrate interior construction;

FIGURE 2 is an axial sectional view. through the compressor wherein the rotor elements are shown in section;

7 of complemental casing components 2 and .4, and referring to FIGURE 1, it will be seen that the component 2 has ashell generally resembling a truncated pan and the component 4 a shell generally cup-like in shape. Each shell has a flanged rim outfitted with bolt holes 6 so that when the two shells are laid end-to-end they can be bolted togethe'rby bolts 6 as seen in FIGURES'Z and 3. Each also has an axial extension that houses a 'pair of shaft bearings 8. The ends of the extensions are externally threaded to accommodate screw caps 16 the upper of which in FIGURE 1 i-s adapted to pass ashaft for reasons which will become apparent. The pan-shaped component 2 is also. provided with a manifold-12 that defines a pair of ports 14 and '16 for the entry and exit of a fluid with respect tothe chamber 15 defined by the assembled components (FIGURES 2 and 3). V

The operating core of the device is formed by a pair of rotors 18 and 29 which are keyed or otherwise fixed on shafts 22 and 24 for rotational mounting in the chamber 15, on the intersecting axes of the journals provided by the shaft bearings 8. Due to the truncation of the component 2 with respect to the component 4, the journal axes are inclined to one another at an acute angle, thus leaving the rotor shafts similarly inclined. The rotor '18 has the shape of a thickened disc one end 36 of which has been centrally or axially relieved to form a hollow 18' (FIGUREZ) resembling the interior of' a dome. The rotor '20, on the other hand, isin the form of a hub having a raised axial d-ome ztl" designed to fit within the hollow 18' of the rotor 18. In the assembly,

the hollow 18 and the dome interiit and complement each other to the extent that they *form a sliding seal between them when the rotors are conjointly rotated.

Such rotation can be accomplished in one of a number of ways, as explained in my aforementioned patent. In the illustrated device, it is accomplished through the use of bevel gears 28 on the interior ends of the shafts, which when assembled, :center about the intersection of the axes of the two shafts and remain continuously in mesh as one or the other of the shafts is rotated. Rotation in this case is effected through drive means (not shown) acting ,on the shaft 22 which projects outside of the upper end cap 10 on the housing. To accommodate the bevel gear arrangement, the dome 20 is opened up at its crown to pass the bevel gear from the rotor 13 and the gears are then engaged within the dome. Moreover, the bottom of the hollow 18' is raised to form a kingpin connection 30 with the opening in the dome. A' dome-like liner 32 is also keyed to the shaft 22 f0 a reason which will be explained shortly." As illustrated,

a single key 34 can be used to key the entire arrangefaces of the rotors and in the assembly cooperatively en- ;gage with one another to forma series of radially oriented cells H at the intervals.

The design of the rotors is also such that when assembled, the cells will undergo volumetric expansion and contraction in accord with a two stage compressor or engine operation. Firstly, their design is such that when assembled, the end faces 26' and 36 of the rotors are substantially centered at the intersection of the axes of their shafts. Additionally, one face 26' has a conical section which is inclined at the aforementioned. acute angle with respect to the other face. As a result, when the rotors are conjointly rotated, the faces alternately converge and diverge between angular stations appearing to the left and the right of the illustration in FIGURES 2 and 3, at which the faces diverge to a maximum and swipe one another or coincide, respectively. Cell expansion occurs therefore on one side of the diametrical plane of these stations, that is, in the upper half revolu- 1 tion of FIGURE 4; and cell contraction on the other side in the lower half revolution of the figure, The former becomes an intake stage when fluid is taken in from the port 14 in FIGURE 4 and the latter a com .pression stage in which the fluid is exhausted through the ports 16. Note also that the two ports are disposed on opposite sidesof the station of coincidence, as established in FIGURES 2 and 3, to communicate with the respective stages early in the former and toward the end of the latter. 7

dome rotates in a socket 33 at the end of chamber 1521s defined bythe shell 2. Coupled with this, the periphery of the disc rotor 18 is cooperatively engaged with the liner 32 in forming a rotational seal which has a labyrinth configuration like that formed between each of the dome 2i) and the hollow 18','and the disc 26 and the socket 38, so that together'the rotors form a substantially fluid-tight annular operating well W with the chamber wall portion '3? lying between the socket and the periphery of the disc rotor. Each of these seals can be formed otherwise, for example, as described in my aforementioned patent in connection with the liner '32, and as will be apparent in the case of the other embodiment illustrated herewith. It is only important that as the rotors sweep through the compression side of the well (the lower half revolution in FIGURE 4), the individual integrity of the cells is maintained for maximum compression of the fluid within each.

My patent discloses a means and technique by which a sliding seal can be formed between the grooves and blades 'for this purpose during the compression stage, if not This technique is ema during the intake stage as well. ployed for illustration in the present instance and briefly comprises giving each of the pairs of corresponding grooves and blades mutually opposing concavely shaped walls that terminate in the case of the blade at the tip portion thereof and in the case of the groove at the mouth portion thereof; and correlating this configuration with the aforementioned acute angle so that the locus generated by the blade tip portion conforms with the contour of the concavelyshaped groove wall as the rotors are turned through the compression stage. Clearly other means and techniques can be employed, so long as such a sliding seal is effected between the cells during this stage.

My patent also indicates that according to convention,

the integrity of the cells can be otherwise maintained by closing the chamber wall portion 39 about the imaginary surface generated by the edges 37' of the blades to the extent that a rotational seal is formed between the two. As seen in FIGURES 2-4, this is actually the case with respect to the side section 39 of the wall 39. However, in accord with the present invention, the diameter of the disc base 26 is less than that of this section so as to open up the lower end faces of the cells; and the end section 39" of the wall lying opposite the open ends of the cells about the trough 38, is recessed back from the blades to a greater extent than is required for a rotational seal and in fact sufficiently below the rim 40 of the trough to form an annular channel 42 about the full perimeter of the well.

To prevent fluid from moving freely between the ports and apart from the cells, however, an arcuate shoe, shim or leaf 44 is positioned in the channel across the station of maximum divergence at the left-hand side of FIGURE 2. The leaf is of comparable cross section with the channel and slidably engaged in it, though capable of being fixed in one of several angular positions by means of the threaded set screws 46 extending up through slots 43 in the end section 39" of the wall. Movement to and from these positions varies the compression stroke undergone by the cells before they release the entrained fluid to the channel, which, as seen by FIGURE 4, extends beyond the angular station at which the exhaust port 16 commences. This movement also varies the intake volume in inverse relation to the adjustment made in the compression stroke. Communication between the two sides of the Well at the station of coincidence on the right-hand side of FIGURE 2 is prevented by bolting a partition 59 of comparable cross section across the channel at this station.

If desired, the diameter of the disc base 26 can be reduced to that of the dome 20' so that the lower end faces of the cells are entirely open. The slots 48 and screws 46 are only a convenient means of releasably positioning the leaf in the channel. Other techniques might include an arrangement of a T-slot in the underside of the leaf and a nut-tightened stud bolt in the wall 39", the head of which is engaged in the T-slot to act as a guide for the leaf.

FIGURE 5 illustrates another embodiment of the invention in which the channel is positioned opposite the radial faces of the cells in the side section 39' of the wall, and the exhaust port 16 is now positioned to open into the channel so that as the leaf is moved into the various positions of its range, it lies transverse the opening 16' of the port and effectively controls the size of the opening. Consequently, the eifect of each change in position is not only to vary the compression stroke of the device, but also to vary the s ze of the exhaust port in relation to that of the inlet port. There is therefore a double-action effect in each change so that a shorter range of positions in this embodiment enables the same or a greater range of control than is possible in the embodiment of FIG- URES 1-4. Note, too, that movement of the leaf 44 still varies the intake volume within the well in inverse relation to the adjustment made in the compression stroke, as in the earlier embodiment. structurally, there has been little other change from the earlier embodiment; although it will be noted that in this instance the disc base 26 is of full diameter and does not extend about the full perimeter of the well but instead terminates to each side of the sector 50' of the well occupied by the station of coincidence. The latter prevents the intake and compression fluids from intermixing in the manner of the partition 59 in the earlier embodiment.

It is desirable that the ends of the leaf be given roughly a 45 slope to lessen any tendency to generate turbulence in the fluid flow. It may also be desirable to slope the leaf back along its length from some point adjacent its for ward end, such as at a point one cell in width from the beginning of the end slope, for purposes of acquiring an anti-knock elfect in engine applications. Clearly other modifications can also be made in the channel-leaf ar- Iangement.

The position of the leaf can be adjusted, if desired, while the device is operating. The adjustment may be actuated by hydraulic or piston means, by solenoid means, by a worm drive, or by some other conventional means for controlling an element of this nature. Or the adjustment may be accomplished by hand as illustrated.

It will also be apparent that the entire device is peculiarly susceptible to die-casting as a convenient production technique. Other techniques can be employed, of course.

The device, as improved herein, is peculiarly suited to use as a compressor or engine that requires supercharging under certain operating conditions. Other uses will also appear to workers in the art.

While the invention has been described with reference to certain preferred embodiments, it will be understood that many modifications and additions can be made in and to these embodiments without departing from the scope and spirit of the invention as defined in the claims following.

I claim as my invention:

1. In a rotary device of the character described, a housing defining a walled chamber, grooved disc and bladed hub rotors rotatably mounted in the chamber in end-torelationship with their axes of rotation intersecting one 7 another at an acute angle, said rotors being cooperatively engaged with one another and with one end of the chambar in defining an annular operating well with the chamber wall portion lying between the end of the chamber and the periphery of the disc rotor, the grooves and blades of the rotors being arranged at angular intervals about the opposing end faces of the rotors and cooperatively engaged in forming a series of radially oriented cells at the intervals, said end faces being substantially centered at the intersection of the axes and at least one of the face s having a conical section which is inclined at the aforementioned acute angle with respect to the other face so that when the rotors are conjointly rotated, the faces alternately converge and diverge between opposite angular stations at which they diverge to a maximum and coincide, respectively, thus subjecting the cells to cyclical intake and compression stages of opposite sides of the well, said housing also defining a pair of ports one of which opens into the intake side of the well and terminates in the direction of rotation at a first angular station therein to supply fluid to the cells, and the other of which opens from the compression side of the well and commences in the direction of rotation at a second angular station therein to exhaust the fluid from the cells, said chamber Wall portion being operatively closed throughout the sector of the well lying between the first and second angular stations but at least a part thereof being recessed back from the surface generated by the edges of the blades to the extent that a part-annular channel is formed on the compression side of the well between the blades and the wall portion, said channel extending from an intermediate angular station adjacent to the station of maximum divergence to at least the second angular station so as to communicate with the exhaust port, and an adjustable filler eiement of comparable cross section operatively positioned in the channel adjacent to the intermediate angular station to determine the compression stroke of the device.

2. A rotary device according to claim 1 wherein the filler element i slidable relatively inwardly and outwardly in the channel for purposes of adjusting its position with respect to the second angular station.

3. A rotary device according to claim 2 wherein the channel extends through the station of maximum divergence into the intake side of the well and the filler element is slidably engaged along the length of the channel to move relatively inwardly and outwardly with respect to the compression side of the channel from within the intake side of the channel.

4. A rotary device according to claim 3 wherein the V filler element comprises an arcuate leaf.

channel is positioned opposite the radial faces of the cells,

8. A rotary device according to claim 1 wherein the intermediate angular station coincides with the station of maximum divergence.

. p 9. A rotary device according to claim 1 wherein the exhaust port opens into the channel and the filler element is adjustable to positions transverse the opening of the exhaust port.

10. In a rotary device of the character described, a housing defining a walled chamlber, grooved disc and bladed hub rotors rotatably mounted in the chamber in end-to-end relationship with their axes of rotation intersecting one another at an acute angle, said rotors also being mounted so that the hub portion of the hub rotor is cooperatively engaged with one end of the chamber in forming a rotational seal there-across, the adjacentends of the rotors also being cooperatively engaged in forming asliding' seal thereacross, the periphery of the disc rotor, moreover, being cooperatively engaged with the wall of the chamber in forming a rotational seal thereabout so that the two rotor together define an annular operating well with the chamber wall portion lying between the end of the chamber and the periphery of the disc rotor, the grooves and blades of the rotors being arranged at angularintervals about the opposing end faces ofthe rotors and'cooperatively engaged in forming a series of radially oriented cells at the intervals, said end faces being substantially centered at'the intersection of the axes and at least one of the faces having a conical section which is inclined at the aforementioned acute angle with respect to the other face so that when the rotors are conjointly 8 maximum divergence to at 7 tion so as to communicate with the exhaust port, and an adjustable filler element of comparable cross section operatively positioned in the channel adjacent to the intermediate angular station to determine the compression stroke of the device 7 11. In a rotary device of the character described, a housing defining a walled chamber, grooved disc and bladed hub rotors rotatably mounted in the chamber in rotated, the faces alternately converge and diverge between opposite angular stations at which they diverge to a maximum and coincide, respectively, thus subjecting the cells to cyclical intake and compression stages on opposite sides of the well, said housing also defining a pair of ports 7 one of which opens into the intake side of the well and terminates in the direction of rotationfat a first angular station therein to supply fluid to the cells, and the other of which opens from the compression si'deof the Welland commences in the direction of rotation at a second angular station therein to exhaust the fluid from the cells, said chamber wall portion being operatively closed throughout the sector of the well lying between the first and sec- 7 0nd angular stations but. at least a part thereof being.

recessed back from the surface generated by the edges formed on the compression side of the well between the blades and the wall portion, said channel extending from lar interval-s about the opposing end faces of the rotors and cooperatively engaged in forming a series of radially oriented cells at the intervals, said end faces being substantially centered at the intersection of the axes and at least one of the faces having a conical section which is inclined at theaforementioned acute angle with respect to V the other face so that when the. rotors are conjointly rotated, the faces alternately converge and divergebetween opposite angular, stations at which they diverge to a'maximum and coincide, respectively, thus subjecting the cells to cyclical intake and compression stages on opposite sides of the well, said housing. also defining a pair of ports one of which opens: into the intake side of the well and terminates in the'dir ection of rotation at a first angular station therein to supply fluid, to the cells, and the other of which opens from the compression side of the well and commences in the direction of rotation at a second angular station therein to exhaust the fluid from the cells, said chamber 'Wall. portion being operatively closed throughout the sector of the well lying between the first and second angular stations but at least a part thereof being recessed back from the surface generated by the edges of the blades to the extent that an annular channel is formed about the full'perimeter of the well, and an arcuate leaf of comparable cross section slidably engaged coincidence to prevent the intake and compression fluids.

from intermixing at said station of coincide.

12; A rotary: device according to claim 1, wherein the exhaust port opens into the compression side of the well in a nonrecessed part of the chamber wall portion.

13. A rotary device according to claim 1, wherein the V first angular station is spaced fromthe station of maximum divergence.

' of the blades-to the extent that'a part-annular channel is a an intermediatelangular stationadjacent to the station of i References (Iited by the Examiner UNITED STATES PATENTS 739,207 9/03 Nielsen 103l27 1,912,634 *6/33 Gray 123l2 2,933,663 5/60 Luck 103120 KARL I. ALBRECHT, Primary Examiner. JOSEPH H. BRANSON, 1a,. Examiner.

least the second -angular sta- 

1. IN A ROTARY DEVICE OF THE CHARAXTER DESCRIBED, A HOUSING DEFINING A WALLED CHAMBER, GROOVED DISC AND BLADED HUB ROTORS ROTATABLY MOUNTED IN THE CHAMBER IN END-TORELATIONSHIP WITH THEIR AXES OF ROTATION INTERSECTING ONE ANOTHER AT AN ACUTE ANGLE, SAID ROTORS BEING COOPERATIVELY ENGASGED WITH ONE ANOTHER AND WITH ONE END OF THE CHAMBER IN DEFINING AN ANNULAR OPERATING WELL WITH THE CHAMBER WALL PORTION LYING BETWEEN THE END OF THE CHAMBER AND THE PERIPHERY OF THE DISC ROTOR, THE GROOVES AND BLADES OF THE ROTORS BEING ARRANGED AT ANGULAR INTERVALS ABOUT THE OPPOSING END FACES OF THE ROTORS AND COOPERATIVELY ENGAGED IN FORMING A SERIES OF RADIALLY ORIENTED CELLS AT THE INTERVALS, SAID END FACES BEING SUBSTANTIALLY CENTERED AT THE INTERSECTION OF THE AXES AND AT LEAST ONE OF THE FACES HAVING A CONICAL SECTION WHICH IS INCLINED AT THE AFOREMENTIONED ACUTE ANGLE WITH RESPECT TO THE OTHER FACE SO THAT WHEN THE ROTORS ARE CONJOINTLY ROTATED, THE FACES ALTERNATELY CONVERGE AND DIVERGE BETWEEN OPPOSITE ANGULAR STATIONS AT WHICH THEY DIVERGE TO A MAXIMUM AND COINCIDE, RESPECTIVELY, THUS SUBJECTION THE CELLS TO CYCLICAL INTAKE AND COMPRESSION STAGES OF OPPOSITE SIDES OF THE WELL, SAID HOUSING ALSO DEFINING A PAIR OF PORTS ONE OF WHICH OPENS INTO THE INTAKE SIDE OF THE WELL AND TERMINATES IN THE DIRECTION OF ROTATION AT A FIRST ANGULAR STATION THEREIN TO SUPPLY FLUID TO THE CELLS, AND THE OTHER OF WHICH OPENS FROM THE COMPRESSION SIDE OF THE WELL AND COMMENCES IN THE DIRECTION OF ROTATION AT A SECOND ANGULAR STATION THEREIN TO EXHAUST THE FLUID FROM THE CELLS, SAID CHAMBER WALL PORTION BEING OPERATIVELY CLOSED THROUGHOUT THE SECTOR OF THE WELL LYING BETWEEN THE FIRST AND SECOND ANGULAR STATIONS BUT AT LEAST A PART THEREOF BEING RECESSED BACK FROM THE SURFACE GENERATED BY THE EDGES OF THE BLADES TO THE EXTENT THAT A PART-ANNULAR CHANNEL IS FORMED ON THE COMPRESSION SIDE OF THE WELL BETWEEN THE BLADES AND THE WALL PORTION, SAID CHANNEL EXTENDING FROM AN INTERMEDIATE ANGULAR STATION ADJACENT TO THE STATION OF MAXIMUM DIVERGENCE TO AT LEAST THE SECOND ANGULAR STATION SO AS TO COMMUNICATE WITH THE EXHAUST PORT, AND AN ADJUSTABLE FILLER ELEMENT OF COMPARTABLE CROSS SECTION OPERATIVELY POSITIONED IN THE CHANNEL ADJACENT TO THE INTERMEDIATE ANGULAR STATION TO DETERMINE THE COMPRESSION STROKE OF THE DEVICE. 